This invention relates to the field of crystals as used for frequency control of electronic apparatus and particularly to the frequency stabilization of such crystals.
Since the fundamental reason for using a crystal for frequency control is the ability to control within extremely narrow limits, and since crystals lose that ability at very low temperatures, it is imperative to compensate in some fashion for low ambient temperatures. Several approaches are known in the art, including mechanical structures whereby physical pressure in proportion to the temperature is applied to the crystal for maintaining the correct frequency regardless of temperature. Other methods have included heating the crystal by means of gold or silver heating elements evaporated onto the surface of the crystal, and heating the crystal in an elaborately controlled, single or double "oven" or housing. Crystals may also be frequency stabilized by electronic means, i.e., external circuitry may sense the ambient temperature and automatically adjust circuit values to "tune" the crystal to the correct frequency. All of the known prior art involves high cost or complexity or both.